As a related art control system for charging a drive battery unit for a hybrid vehicle, it is disclosed in, for example, Japanese Patent Provisional Publication No. 2010-81740 (hereinafter is referred to as JP2010-81740). In the control system in JP2010-81740, a resistance element is provided on an extending signal line that extends from a pilot signal line, and it is proposed to judge whether a connector of a charging cable is actually disconnected from a charging inlet of the vehicle or an operation button for releasing the connector of the charging cable from a mechanical lock between the charging inlet and the connector is merely pressed, on the basis of a change of a signal level inputted through the extending signal line.